Flexible display apparatus and touch sensitive display apparatus

ABSTRACT

A flexible display apparatus includes a flexible substrate including a display area and a bending area outside the display area, the bending area to be bent around a bending axis; an inorganic insulating layer on the flexible substrate; a cut unit in the inorganic insulating layer in the bending area; a stress relaxation layer filling the cut unit and extending into the display area; a wiring part on the stress relaxation layer in the bending area; a planarization layer covering the wiring part and on the stress relaxation layer; and a display on the planarization layer in the display area and electrically connected to the wiring part.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation application based on currently pending U.S.patent application Ser. No. 16/216,013, filed Dec. 11, 2018, thedisclosure of which is incorporated herein by reference in its entirety.U.S. patent application Ser. No. 16/216,013 claims priority benefit,under 35 U.S.C. § 119, of Korean Patent Application No. 10-2018-0013437,filed on Feb. 2, 2018 in the Korean Intellectual Property Office, thedisclosure of which is incorporated herein by reference for allpurposes.

BACKGROUND 1. Field

One or more embodiments relate to a flexible display apparatus, and moreparticularly, to a flexible display apparatus having a bending area.

2. Description of the Related Art

Organic light-emitting display apparatuses have a self-emissioncharacteristic, thus no separate light source is needed, allowing athickness and a weight thereof to be reduced. In addition, the organiclight-emitting display apparatuses have high-grade characteristics suchas low power consumption, high brightness, and a quick response speed.

An organic light-emitting display apparatus includes a substrate, athin-film transistor on the substrate, an organic light-emitting deviceof which emission is controlled by the thin-film transistor, and aplurality of insulation layers arranged among electrodes forming thethin-film transistor. Recently, organic light-emitting displayapparatuses including a flexible substrate and having a bending areahave been developed.

SUMMARY

According to one or more embodiments, a flexible display apparatusincludes: a flexible substrate including a display area and a bendingarea outside the display area, the bending area to be bent around abending axis; an inorganic insulating layer on the flexible substrate; acut unit in the inorganic insulating layer in the bending area; a stressrelaxation layer filling the cut unit and extending into the displayarea; a wiring part on the stress relaxation layer in the bending area;a planarization layer covering the wiring part and on the stressrelaxation layer; and a display on the planarization layer in thedisplay area and electrically connected to the wiring part.

The inorganic insulating layer may include a plurality of inorganicfilms.

In the display area, the planarization layer may be on the stressrelaxation layer.

The cut unit may extend in a direction parallel to the bending axis.

The stress relaxation layer may include an organic insulating material.

A thickness of the stress relaxation layer in the cut unit may begreater than a depth of the cut unit.

A lower surface of the stress relaxation layer in the cut unit may comein direct contact with an upper surface of the flexible substrate.

The flexible display apparatus may further include a thin-filmtransistor electrically connecting the display to the wiring part and inthe display area, wherein a distance from an upper surface of theplanarization layer to the flexible substrate in a region overlappingthe thin-film transistor may be substantially the same as a distancefrom the upper surface of the planarization layer to the flexiblesubstrate in a region overlapping the cut unit.

The planarization layer may include an organic insulating material.

The flexible display apparatus may further include a thin-filmtransistor electrically connecting the display to the wiring part and inthe display area, wherein an upper surface of the uppermost electrode ofthe thin-film transistor is higher than an upper surface of the stressrelaxation layer.

The wiring part may include the same material as the uppermost electrodeof the thin-film transistor.

The flexible display apparatus may further include, in the display area,a thin-film transistor electrically connecting the display to the wiringpart, wherein an upper surface of the uppermost electrode of thethin-film transistor is lower than or equal to an upper surface of thestress relaxation layer.

The wiring part may include the same material as the uppermost electrodeof the thin-film transistor.

The stress relaxation layer may have an opening and the uppermostelectrode of the thin-film transistor may be in the opening.

The flexible substrate may include: a first substrate including apolymer resin; a second substrate on the first substrate and including apolymer resin; and a barrier film between the first substrate and thesecond substrate.

In the cut unit, the lower surface of the stress relaxation layer maycome in direct contact with an upper surface of the second substrate.

The flexible display apparatus may further include an encapsulation partcovering the display and including at least one inorganic film and atleast one organic film.

According to one or more embodiments, a touch-detecting displayapparatus includes: a flexible substrate including a display area and abending area outside the display area, the bending area to be bentaround a bending axis; an inorganic insulating layer on the flexiblesubstrate; a stress relaxation layer filling a cut unit in the inorganicinsulating layer in the bending area, and extending into the displayarea; a wiring part on the stress relaxation layer in the bending area;a planarization layer covering the wiring part and on the stressrelaxation layer; a display on the planarization layer in the displayarea and electrically connected to the wiring part; a flexibleencapsulation part covering the display; a touch detection layer on theflexible encapsulation part; color filters on the touch detection layer;and a black matrix between the color filters.

The display may include a first electrode, an organic light-emittinglayer, and a second electrode, and a tilt angle of the first electrodewith a plane parallel to the flexible substrate may be smaller than0.1°.

The color filters and the black matrix may share an overlapping area.

In the display area, the planarization layer may be on the stressrelaxation layer.

A pad electrode electrically connected to the wiring part may be at anedge of the flexible substrate, and when the bending area is folded, thepad electrode may overlap the display area.

In the cut unit, a thickness of the stress relaxation layer may begreater than a depth of the cut unit.

The touch-detecting display apparatus further include, in the displayarea, a thin-film transistor electrically connecting the display to thewiring part, wherein a distance from an upper surface of theplanarization layer to the flexible substrate in a region overlappingthe thin-film transistor may be substantially the same as a distancefrom the upper surface of the planarization layer to the flexiblesubstrate in a region overlapping the cut unit.

Other aspects, features, and advantages other than those described abovewill be clear from the detailed description, the claims, and thedrawings below to carry out the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

Features will become apparent to those of skill in the art by describingin detail exemplary embodiments with reference to the attached drawingsin which:

FIG. 1 illustrates a schematic perspective view of a flexible displayapparatus according to a first embodiment;

FIG. 2 illustrates a schematic cross-sectional view of the flexibledisplay apparatus shown in FIG. 1;

FIG. 3 illustrates a schematic perspective view showing an unfoldedstate of the flexible display apparatus shown in FIG. 1;

FIG. 4 illustrates a schematic cross-sectional view showing a displayarea DA and a bending area BA of the flexible display apparatus shown inFIG. 1;

FIG. 5 illustrates a schematic cross-sectional view showing a displayarea DA and a bending area BA of a flexible display apparatus accordingto a comparative example;

FIG. 6 illustrates color separation degrees of external light accordingto tilt angles when a pixel electrode of a green light-emitting pixel istilted from a surface parallel to a flexible substrate;

FIG. 7A illustrates an image showing a phenomenon that a reflectivecolor of external light is separated when a tilt angle of the pixelelectrode exceeds 1.0°;

FIG. 7B illustrates an image showing a phenomenon that a reflectivecolor of external light is separated when a tilt angle of the pixelelectrode is smaller than 1.0°;

FIG. 8 illustrates a schematic cross-sectional view showing a displayarea DA and a bending area BA of a flexible display apparatus accordingto a second embodiment;

FIG. 9 illustrates a schematic cross-sectional view showing a displayarea DA and a bending area BA of a flexible display apparatus accordingto a third embodiment; and

FIG. 10 illustrates a schematic cross-sectional view showing a displayarea DA and a bending area BA of a flexible display apparatus accordingto a fourth embodiment.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments, examples of whichare illustrated in the accompanying drawings, wherein like referencenumerals refer to like elements throughout. In this regard, the presentembodiments may have different forms and should not be construed asbeing limited to the descriptions set forth herein. Accordingly, theembodiments are merely described below, by referring to the figures, toexplain aspects of the present description.

When it is described through the embodiments that a certain element,such as a layer, a film, a region, or a substrate, is located “on”another element, it may be understood that the certain element may belocated “on” another element directly or via another element in themiddle. In addition, for convenience of description, in the accompanyingdrawings, sizes of components may be exaggerated or reduced. Forexample, the size and the thickness of each component shown in thedrawings are arbitrarily shown for convenience of description, and thusthe present disclosure is not necessarily limited thereto.

In the embodiments, an x axis, a y axis, and a z axis are not limited tothree axes of a rectangular coordinate system but may be analyzed as awide meaning including the same. For example, the x axis, the y axis,and the z axis may be orthogonal to each other or may indicate differentdirections that are not orthogonal to each other.

FIG. 1 is a schematic perspective view of a flexible display apparatus100 according to a first embodiment. FIG. 2 is a schematiccross-sectional view of the flexible display apparatus 100 shown inFIG. 1. FIG. 3 is a schematic perspective view showing an unfolded stateof the flexible display apparatus 100 shown in FIG. 1. FIG. 4 is aschematic cross-sectional view showing a display area DA and a bendingarea BA of the flexible display apparatus 100 shown in FIG. 1.

Referring to FIGS. 1 to 4, the flexible display apparatus 100 accordingto an embodiment may include a flexible substrate 110, a display 120formed on the flexible substrate 110, an inorganic insulating layer 130,a stress relaxation layer 140, a wiring part 150, a planarization layer160, and an encapsulation part 210. In addition, the flexible displayapparatus 100 may further include a pad electrode 170, a chip on film(COF) 180, and a printed circuit board (PCB) 190.

In the present embodiment, the flexible substrate 110 includes thedisplay area DA in which the display 120 is formed, and includes thebending area BA extending in a first direction (+y direction) in anon-display area NDA outside the display area DA and bent around abending axis BAX.

The flexible substrate 110 may include various materials having aflexible or bendable characteristic, e.g., a polymer resin such aspolyethersulphone, polyacrylate, polyetherimide, polyethylenenaphthalate, polyethyleneterephthalate, polyphenylene sulfide,polyarylate, polyimide, polycarbonate, cellulose acetate propionate, andthe like. The flexible substrate 110 may also be variously modified suchthat the flexible substrate 110 may have a multi-layer structureincluding two layers including such a polymer resin and a barrier layerbetween the two layers, e.g., an inorganic material such as siliconoxide, silicon nitride, or silicon oxynitride.

The display 120 includes a plurality of pixels and displays an image bycombining light emitted from the plurality of pixels. Each pixel mayinclude a pixel circuit and an organic light-emitting device. The pixelcircuit may include at least two thin-film transistors and at least onecapacitor to control light emission of the organic light-emittingdevice. A detailed structure of the display 120 will be described later.

The bending area BA may be a portion of the non-display area NDA. Aplurality of pad electrodes 170 may be formed at an edge of the flexiblesubstrate 110 extending from the bending area BA in a second direction(+x direction). The wiring part 150 including signal lines such as scanlines and data lines electrically connected to the plurality of pixelsand power lines such as driving voltage lines are electrically connectedto the pad electrodes 170.

The pad electrodes 170 may be connected to the COF 180. The COF 180 maybe replaced by a flexible printed circuit (FPC). The COF 180 may beconnected to the PCB 190.

The COF 180 may include an output wiring part 181, a driving chip 183,and an input wiring part 182. The PCB 190 is connected to the inputwiring part 182 of the COF 180 and inputs, to the COF 180, a controlsignal for controlling the driving chip 183 of the COF 180. The outputwiring part 181 of the COF 180 is connected to the pad electrodes 170and outputs, to the pad electrodes 170, power and various kinds ofsignals for controlling display of the flexible display apparatus 100.

When the non-display area NDA including the wiring part 150 and the padelectrodes 170 is located alongside the display area DA without beingbent (see FIG. 3), an area of a dead space outside the display 120increases. The flexible display apparatus 100 according to the presentembodiment has the bending area BA formed by bending a portion of thenon-display area NDA in which the wiring part 150 extends. As a bendingresult, the edge of the flexible substrate 110, on which the padelectrodes 170 are formed, overlaps the display area DA at the rear ofthe display area DA. Thus the dead space outside the display 120 isminimized.

The bending area BA is bent around the bending axis BAX. The center ofcurvature of the bending area BA is located on the bending axis BAX.Referring to FIGS. 1 and 2, the bending axis BAX is parallel to the yaxis.

The inorganic insulating layer 130 including at least one inorganic filmamong a barrier film 131, a buffer film 132, a gate insulating film 133,a first interlayer insulating film 134, and a second interlayerinsulating film 135 on the flexible substrate 110. The inorganicinsulating layer 130 may be between electrodes and wirings included inthe display 120 to insulate the same.

In the present embodiment, the inorganic insulating layer 130 in thebending area BA may have a cut unit CU that extends in a direction(y-axis direction) parallel to the bending axis BAX. The cut unit CU maybe filled with the stress relaxation layer 140 including an organicinsulating material. The stress relaxation layer 140 extends into thedisplay area DA. For example, as may be seen in FIG. 4, the stressrelaxation layer 140 is on the inorganic insulating layer 130 in thedisplay area DA, i.e., between the inorganic insulating layer 130 andthe planarization layer 160. In particular, in the display area DA, theplanarization layer 160 may be on, e.g., in direct contact with, thestress relaxation layer 140.

The wiring part 150 may be on the stress relaxation layer 140 in thenon-display area NDA. The wiring part 150 may include a metal material.The inorganic insulating layer 130 has much less flexibility than thewiring part 150, e.g., may be sufficiently brittle that it may be brokenby an external force. Therefore, if the inorganic insulating layer 130is in the bending area BA, cracks may occur therein by a tensile forcedue to bending. These cracks may be propagated to other regions of theinorganic insulating layer 130. The cracks in the inorganic insulatinglayer 130 may cause the wiring part 150 to be disconnected, therebycausing abnormal display of the flexible display apparatus 100.

In the present embodiment, the stress relaxation layer 140 is formed ofa material having lower brittleness and higher flexibility than theinorganic insulating layer 130. For example, the stress relaxation layer140 may be formed of an organic insulating material, e.g., acryl, epoxy,acrylate, polyimide, benzocyclobutene (BCB), or hexamethyldisiloxane(HMDSO). The stress relaxation layer 140 may be formed by filling thecut unit CU and closely attaching to side walls of the cut unit CU suchthat there is no gap between the stress relaxation layer 140 and theinorganic insulating layer 130.

In addition, in the present embodiment, the stress relaxation layer 140may have a lower surface that comes in direct contact with not only theside walls of the cut unit CU but also an upper surface of the flexiblesubstrate 110, which is a lower surface of the cut unit CU. Thus, anadhesive force with the flexible substrate 110 is also improved.

Therefore, the flexible display apparatus 100 according to the presentembodiment may suppress the occurrence of cracks in the inorganicinsulating layer 130 due to bending stress and prevent disconnection ofthe wiring part 150, by forming the cut unit CU in the inorganicinsulating layer 130 in the bending area BA and forming the stressrelaxation layer 140 having low brittleness in the cut unit CU.

In more detail, the barrier film 131 may be on the flexible substrate110. The barrier film 131 blocks infiltration of moisture and oxygenthrough the flexible substrate 110 and may be formed of a multi-layerfilm in which silicon oxide (SiO₂) and silicon nitride (SiN_(x)) arealternately and repetitively stacked.

The buffer film 132 may be on the barrier film 131. The buffer film 132provides a planar surface for forming a pixel circuit thereon and mayinclude SiO₂ or SiN_(x).

A semiconductor layer 121 and a first capacitor electrode 125 are on thebuffer film 132. The semiconductor layer 121 may be a polysilicon oroxide semiconductor, and the semiconductor layer 121 may be an oxidesemiconductor, which may be covered by a separate protective film. Thesemiconductor layer 121 may include a channel region that is undoped,and a source region and a drain region located at both sides of thechannel region and doped with impurities. The first capacitor electrode125 may include the same material as the semiconductor layer 121.

The gate insulating film 133 is on the semiconductor layer 121 and thefirst capacitor electrode 125. The gate insulating film 133 may beformed of a single film of SiO₂ or SiN_(x) or a stacked film thereof.

A gate electrode 122 and a second capacitor electrode 126 are formed onthe gate insulating film 133. The gate electrode 122 overlaps thechannel region of the semiconductor layer 121. The second capacitorelectrode 126 may include the same material as the gate electrode 122.

The first interlayer insulating film 134 is formed on the gate electrode122 and the second capacitor electrode 126, and a third capacitorelectrode 127 may be formed on the first interlayer insulating film 134.The third capacitor electrode 127 may include the same material as thegate electrode 122.

The gate insulating film 133 forms a first dielectric film between thefirst capacitor electrode 125 and the second capacitor electrode 126,and the first interlayer insulating film 134 forms a second dielectricfilm between the second capacitor electrode 126 and the third capacitorelectrode 127, thereby forming a storage capacitor 202.

The second interlayer insulating film 135 may be on the third capacitorelectrode 127, and a source electrode 123 and a drain electrode 124 maybe on the second interlayer insulating film 135. The first and secondinterlayer insulating films 134 and 135 may be formed of a single filmof SiO₂ or SiN_(x) or a stacked film thereof.

The source electrode 123 and the drain electrode 124 in the display areaDA are respectively connected to the source region and the drain regionof the semiconductor layer 121 through contact holes formed in the gateinsulating film 133, the first and second interlayer insulating films134 and 135, and the stress relaxation layer 140. Thus, the sourceelectrode 123 and the drain electrode 124 may be on, e.g., directly on,the stress relaxation layer 140. Therefore, the source electrode 123 andthe drain electrode 124 are higher than an upper surface of the stressrelaxation layer 140.

The wiring part 150 in the bending area BA may be formed of the samematerial as that of the source electrode 123 and the drain electrode124. The source electrode 123, the drain electrode 124, and the wiringpart 150 may be formed of a metal multi-layer film, e.g., molybdenum(Mo)/aluminum (Al)/Mo or titanium (Ti)/Al/Ti.

The pixel electrode 141 is formed on the planarization layer 160 foreach pixel and is connected to the drain electrode 124 of a drivingthin-film transistor 201 through the via hole VH formed in theplanarization layer 160. The driving thin-film transistor includes thesemiconductor layer 121, the gate electrode 122, the source electrode,and the drain electrode 124.

In addition to the driving thin-film transistor 201 and the storagecapacitor 202, the pixel circuit may also include a switching thin-filmtransistor.

The planarization layer 160 is disposed on the driving thin-filmtransistor 201 and the wiring part 150. The driving thin-film transistor201 is connected to an organic light-emitting device 203 and drives theorganic light-emitting device 203. The planarization layer 160 mayinclude an organic insulating material or an inorganic insulatingmaterial or may be in a composite form of the organic insulatingmaterial and the inorganic insulating material.

The organic light-emitting device 203 may include a pixel electrode 141,an emission layer 142, and a common electrode 143.

The pixel electrode 141 is formed on the planarization layer 160 foreach pixel and is connected to the drain electrode 124 of the drivingthin-film transistor 201 through a via hole VH formed in theplanarization layer 160.

A pixel defining film 204 is formed on an upper part of theplanarization layer 160 and an edge of the pixel electrode 141. Thepixel defining film 204 defines a pixel with an opening through which acentral part of the pixel electrode 141 is exposed. In addition, thepixel defining film 204 prevents the occurrence of an arc and the likeat the edge of the pixel electrode 141 by increasing a distance betweenthe edge of the pixel electrode 141 and the common electrode 143 on anupper part of the pixel electrode 141. The pixel defining film 204 maybe formed of an organic material such as polyimide or HMDSO.

The emission layer 142 may be on the pixel electrode 141, and the commonelectrode 143 may be all over the display area DA regardless of pixel.

FIG. 4 shows only the emission layer 142 on an upper part of the pixelelectrode 141, but an intermediate layer besides the emission layer 142may be further included between the pixel electrode 141 and the commonelectrode 143. The intermediate layer of the organic light-emittingdevice 203 may include a low or high molecular material. When theintermediate layer includes a low molecular material, the intermediatelayer may have a structure in which a hole injection layer (HIL), a holetransport layer (HTL), an emission layer (EML), an electron transportlayer (ETL), an electron injection layer (EIL), and the like are stackedin a single or composite structure, and may include various organicmaterials, e.g., including copper phthalocyanine (CuPc),N,N′-Di(naphthalene-1-yl)-N,N′-diphenyl-benzidine (NPB),tris-8-hydroxyquinoline aluminum (Alq3), and the like. These layers maybe formed by a vacuum deposition method.

When the intermediate layer includes a high molecular material, theintermediate layer may mainly have a structure including an HTL and anEML. In this case, the HTL may include polyethylenedioxythiophene(PEDOT), and the EML may include a high molecular material of apoly-phenylenevinylene (PPV) group, a polyfluorene group, or the like.The intermediate layer may be formed by screen printing, inkjetprinting, laser induced thermal imaging (LITI), or the like.

Any one of the pixel electrode 141 and the common electrode 143 injectsholes into the emission layer 142, and the other one thereof injectselectrons into the emission layer 142. The electrons and the holes arebonded in the emission layer 142 such that excitons are generated, andlight is emitted by energy generated when the excitons transit from anexcited state to a ground state.

The pixel electrode 141 may be formed of a reflective film, and thecommon electrode 143 may be formed of a transparent film or atranslucent film. The light emitted from the emission layer 142 isreflected from the pixel electrode 141, transmits through the commonelectrode 143, and then is output to the outside. When the commonelectrode 143 is formed of a translucent film, a portion of the lightreflected from the pixel electrode 141 is re-reflected from the commonelectrode 143, and the pixel electrode 141 and the common electrode 143may form a resonance structure, thereby increasing light extractionefficiency.

The organic light-emitting device 203 is covered by the encapsulationpart 210. The encapsulation part 210 may seal the organic light-emittingdevice 203 such that deterioration of the organic light-emitting device203 due to moisture and oxygen included in external air is suppressed.The encapsulation part 210 may have a stacked structure of an inorganicmaterial and an organic material and may include, e.g., a firstinorganic film 211, an organic film 212, and a second inorganic film213.

Referring again to the stress relaxation layer 140, as shown in FIG. 4,in the present embodiment, the stress relaxation layer 140 fills the cutunit CU and extends into the display area DA. Thus, a thickness T of thestress relaxation layer 140 filling the cut unit CU of the inorganicinsulating layer 130 may be greater than a depth D of the cut unit CU.Therefore, the wiring part 150 may be in direct contact with the stressrelaxation layer 140, not with the inorganic insulating layer 130.

FIG. 5 is a schematic cross-sectional view showing a display area DA anda bending area BA of a flexible display apparatus 10 according to acomparative example. Referring to FIG. 5, unlike the present embodiment,in the flexible display apparatus 10 according to the comparativeexample, a stress relaxation layer 140′ including an organic insulatingmaterial fills a cut unit CU, but the stress relaxation layer 140′ doesnot extend to the display area DA. As shown in FIG. 5, the planarizationlayer 160 and the inorganic insulating layer 130 are in direct contactwith each other in the bend area BA outside the cut unit CU. Therefore,the thickness T of the stress relaxation layer 140′ in the cut unit CUof the inorganic insulating layer 130 cannot be greater than the depth Dof the cut unit CU.

In the flexible display apparatus 10 according to the comparativeexample of FIG. 5, the stress relaxation layer 140′ filling the cut unitCU in the bending area BA does not extend to the display area DA and aplanarization layer 160′ may be different than the planarization layer160 of FIG. 4. Since the stress relaxation layer 140′ is not in thedisplay area DA in FIG. 5, the source electrode 123 and the drainelectrode 124 are respectively connected to the source region and thedrain region of the semiconductor layer 121 through contact holes in thefirst and second interlayer insulating films 134 and 135 and the gateinsulating film 133. Otherwise, elements of FIG. 5 are the same as thoseof FIG. 4, and description thereof will not be repeated.

As described above, unlike the comparative example, in the flexibledisplay apparatus 100 according to the present embodiment, a differencebetween the thickness T of the stress relaxation layer 140 filling thecut unit CU and the depth D of the cut unit CU may prevent colorseparation of reflective light reflected from a light-emitting device ofthe display 120, as described in detail below.

External light incident to the organic light-emitting device 203 fromthe outside of the flexible display apparatus 10 is emitted by beingreflected from various kinds of electrodes and wirings located insidethe flexible display apparatus 10. The reflected external light may bemixed with light emitted from the emission layer 142, thereby causingnoise. Particularly, according to flatness of the pixel electrode 141acting as a reflective electrode, a color separation phenomenon of thereflected external light may be affected.

The flatness of the pixel electrode 141 depends on flatness of theplanarization layer 160 in direct contact with the pixel electrode 141.The flatness of the planarization layer 160 may depend on a design of athin-film transistor, a capacitor, and wirings arranged at a lower partof the planarization layer 160.

In the flexible display apparatus 10 according to the comparativeexample, the planarization layer 160 is formed to make the display 120flat. However, due to a level difference by a structure of the thin-filmtransistor, the capacitor, and the wirings arranged at a lower part ofthe planarization layer 160, a tilt angle θ (see FIG. 6) of the pixelelectrode 141 with a plane parallel to the flexible substrate 110exceeds 1.0°.

However, referring to FIG. 4, the flexible display apparatus 100according to the present embodiment has the stress relaxation layer 140including an organic insulating material at a lower part of theplanarization layer 160 and also extends to the display area DA. Thus, alevel difference by a structure of a thin-film transistor, a capacitor,and wirings arranged at a lower part of the stress relaxation layer 140is alleviated. Since the planarization layer 160 is formed in a state inwhich the level difference is alleviated, the tilt angle θ of the pixelelectrode 141 with a plane parallel to the flexible substrate 110 doesnot exceed 1.0°. That is, an upper surface of the planarization layer160 is substantially flat.

Therefore, according to the present embodiment, a distance from theupper surface of the planarization layer 160 to the flexible substrate110 in a region overlapping the driving thin-film transistor 201 may besubstantially the same as a distance from the upper surface of theplanarization layer 160 to the flexible substrate 110 in a regionoverlapping the cut unit CU.

FIG. 7A illustrates an image showing a phenomenon that a reflectivecolor of external light is separated when a tilt angle of the pixelelectrode 141 exceeds 1.0°. That is, reflected external lights are notmixed to emit white light but separated to respective unique colors,thereby generating noise.

FIG. 7B illustrates an image showing a phenomenon that a reflectivecolor of external light is separated when a tilt angle of the pixelelectrode 141 is smaller than 1.0°. Although color separation ofreflected external lights does not fully disappear, the color separationis significantly alleviated when compared with FIG. 7A.

FIG. 6 illustrates color separation degrees of external light accordingto tilt angles when the pixel electrode 141 of a green light-emittingpixel is tilted from a surface parallel to a flexible substrate.

(a) of FIG. 6 shows relative locations of a red band R and a green bandGa of reflected external light when the tilt angle θ is 0.5°, (b) ofFIG. 6 shows relative locations of the red band R and the green band Gaof reflected external light when the tilt angle θ is t1.0°, and (c) ofFIG. 6 shows relative locations of the red band R and the green band Gaof reflected external light when the tilt angle θ is 1.9°.

A difference of the green band Ga based on the red band R in (a) of FIG.6 is Δa, a difference of the green band Ga based on the red band R in(b) of FIG. 6 is Δb, and a difference of the green band Ga based on thered band R in (c) of FIG. 6 is Δc. A color separation phenomenonincreases from (a) of FIG. 6 to (c) of FIG. 6, i.e., as the tilt angle θincreases.

In the present embodiment, since the stress relaxation layer 140 extendsinto the display area DA, roughness due to a thin-film transistor, acapacitor, and wirings arranged at a lower part of the pixel electrode141 may be reduced. Since the planarization layer 160 is on the stressrelaxation layer 140, a tilt angle of the pixel electrode 141 may bereduced.

Therefore, the flexible display apparatus 100 according to the presentembodiment may have the bending area BA to reduce a dead space. Inaddition, by forming the cut unit CU in the bending area BA and fillingthe stress relaxation layer 140 therein, cracks in an inorganicinsulating layer and disconnection of a wiring may be prevented. Inaddition, by reducing a tilt angle of the pixel electrode 141 by havingthe stress relaxation layer 140 extending into the display area DA,color separation of external light may be prevented, thereby increasingdisplay quality.

Hereinafter, various embodiments of the present disclosure will bedescribed with reference to FIGS. 8 to 10.

FIG. 8 is a schematic cross-sectional view showing a display area DA anda bending area BA of a flexible display apparatus 200 according to asecond embodiment. A description will be made based on differences whencompared with FIG. 4 showing the flexible display apparatus 100according to the first embodiment. Like reference numerals in FIG. 4refer to like elements in FIG. 4.

The flexible display apparatus 200 according to the second embodimentdiffers from the flexible display apparatus 100 according to the firstembodiment with respect to a pattern of the stress relaxation layer 140in the display area DA. According to the present embodiment, a stressrelaxation layer 140 a filling the cut unit CU of the bending area BAand simultaneously extends into the display area DA, but an opening OP1is in the stress relaxation layer 140 a to expose a location where thesource electrode 123 and the drain electrode 124.

The source electrode 123 and the drain electrode 124 are formed in theopening OP1 such that upper surfaces of the source electrode 123 and thedrain electrode 124 are not higher than an upper surface of the stressrelaxation layer 140 a, e.g., may be lower than the upper surface of thestress relaxation layer 140 a. Thus, the source electrode 123 and thedrain electrode 124 are not on the stress relaxation layer 140 a. Whenthe source electrode 123 and the drain electrode 124 are formed, thewiring part 150 may also formed simultaneously on the stress relaxationlayer 140 a.

The planarization layer 160 is formed on the source electrode 123, thedrain electrode 124, and the wiring part 150, and the drain electrode124 is connected to the pixel electrode 141 through a via hole VH formedin the planarization layer 160.

Since the source electrode 123 and the drain electrode 124 are formed inthe opening OP1, roughness due to the source electrode 123 and the drainelectrode 124 arranged at a lower part of the pixel electrode 141 issmall. Thus, a tilt angle of the pixel electrode 141 may be furtherreduced when compared with the first embodiment.

FIG. 9 is a schematic cross-sectional view showing a display area DA anda bending area BA of a flexible display apparatus 300 according to athird embodiment. A description will be made based on differences whencompared with FIG. 4 showing the flexible display apparatus 100according to the first embodiment. Like reference numerals in FIG. 4refer to like elements in FIG. 4.

The flexible display apparatus 300 according to the third embodimentdiffers from the flexible display apparatus 100 according to the firstembodiment in that the flexible display apparatus 300 further includes atouch layer 220, color filters 240, a black matrix 230, and a protectivelayer 250 on the encapsulation part 210.

The touch layer 220 includes a first insulating layer 221 formed on theencapsulation part 210, a second insulating layer 222 formed on thefirst insulating layer 221, and a plurality of touch electrodes 223formed between the first insulating layer 221 and the second insulatinglayer 222. Alternatively, the touch layer 220 may include variouselectrode structures, e.g., a mesh electrode pattern and a transparentsegment electrode.

The touch layer 220 may detect a touch input based on a mutualcapacitance change caused by the touch input. That is, when a touchinput is applied, a mutual capacitance is changed by the touch input,and a touch detector connected to the touch layer 220 may detect alocation at which the mutual capacitance is changed, thereby detectingthe touch input

The color filters 240 and the black matrix 230 are arranged on the touchlayer 220. The black matrix 230 overlaps a non-emission region of apixel, and the color filters 240 overlap emission regions, respectively.The color filters 240 may include red color filters 242, green colorfilters 241, and blue color filters 243.

The black matrix 230 includes a material capable of blocking light. Forexample, the black matrix 230 may include an organic material havinghigh light absorption ratio. The black matrix 230 may include a blackpigment or a black dye. The black matrix 230 includes a light-sensitiveorganic material, e.g., may include a coloring agent such as a pigmentor a dye. The black matrix 230 may have a single- or multi-layerstructure.

Although FIG. 9 shows that the color filters 240 cover a portion of theblack matrix 230, according to a forming sequence of the black matrix230 and the color filters 240, the black matrix 230 may cover a portionof the color filters 240, or the color filters 240 may cover a portionof the black matrix 230.

The color filters 240 may not only transmit light generated by theorganic light-emitting device 203 to the outside but also reduce areflectance of light incident from the outside. When external lightpasses through the color filters 240, light intensity of the externallight is reduced to about one third thereof.

A portion of the light which has passed through the color filters 240 isextinguished, and the remaining portion of the light is reflected fromcomponents arranged under the color filters 240, for example, athin-film transistor, a capacitor, wirings, the encapsulation part 210,and the like arranged at a lower part of the pixel electrode 141.

The reflected light is incident to the color filters 240, and brightnessof the reflected light is reduced while passing through the colorfilters 240. As a result, since only a portion of the external light isreflected and discharged from the flexible display apparatus 300,external light reflection may be reduced.

In addition, according to the present embodiment, since not onlyexternal light reflection is reduced by using the color filters 240 andthe black matrix 230 but also a polarizing film generally used to reduceexternal light reflection does not have to be used, a thickness of theflexible display apparatus 300 may be reduced. In addition, a thindisplay apparatus may be manufactured, and the present embodiment may beused for a foldable or bendable display apparatus.

As described above, compared with the flexible display apparatus 100according to the first embodiment in FIG. 4, the flexible displayapparatus 300 including the color filters 240 and the black matrix 230may reduce external light reflection, but a tilt angle of the pixelelectrode 141 functioning as a reflective electrode still affectsexternal light reflection of the flexible display apparatus 300.According to the present embodiment, since the stress relaxation layer140 extends into the display area DA, roughness due to a thin-filmtransistor, a capacitor, and wirings arranged at a lower part of thepixel electrode 141 may be small, and since the planarization layer 160is once more formed on the stress relaxation layer 140, a tilt angle ofthe pixel electrode 141 may be reduced, thereby much efficientlyreducing external light reflection.

FIG. 10 is a schematic cross-sectional view showing a display area DAand a bending area BA of a flexible display apparatus 400 according to afourth embodiment. A description will be made based on differences whencompared with FIG. 9 showing the flexible display apparatus 300according to the third embodiment. Like reference numerals refer to likeelements.

The flexible display apparatus 400 according to the fourth embodimentdiffers from the flexible display apparatus 300 according to the thirdembodiment with respect to a pattern of the stress relaxation layer 140formed in the display area DA. According to the present embodiment, thestress relaxation layer 140 a fills the cut unit CU of the bending areaBA and simultaneously extends to the display area DA, but the openingOP1 is in the stress relaxation layer 140 a to expose a location wherethe source electrode 123 and the drain electrode 124 are formed.

The source electrode 123 and the drain electrode 124 are formed in theopening OP1 such that upper surfaces of the source electrode 123 and thedrain electrode 124 are not higher than an upper surface of the stressrelaxation layer 140 a. When the source electrode 123 and the drainelectrode 124 are formed, the wiring part 150 is also formed together onthe stress relaxation layer 140 a.

The planarization layer 160 is formed on the source electrode 123, thedrain electrode 124, and the wiring part 150, and the drain electrode124 is connected to the pixel electrode 141 through a via hole VH formedin the planarization layer 160. Since the source electrode 123 and thedrain electrode 124 are formed in the opening OP1, roughness due to thesource electrode 123 and the drain electrode 124 arranged at a lowerpart of the pixel electrode 141 is small, and thus a tilt angle of thepixel electrode 141 may be further reduced when compared with the thirdembodiment.

A flexible display apparatus, according to an embodiment, may have abending area formed outside a display area, thereby reducing a deadspace. A cut unit filled with a stress relaxation layer may be in thebending area. Thus, cracks in an inorganic insulating layer anddisconnection of a wiring may be prevented.

In addition, the flexible display apparatus, according to an embodiment,may have the stress relaxation layer extending into the display area toreduce a tilt angle of a pixel electrode, such that color separation ofexternal light is prevented, thereby increasing display quality.

Example embodiments have been disclosed herein, and although specificterms are employed, they are used and are to be interpreted in a genericand descriptive sense only and not for purpose of limitation. In someinstances, as would be apparent to one of ordinary skill in the art asof the filing of the present application, features, characteristics,and/or elements described in connection with a particular embodiment maybe used singly or in combination with features, characteristics, and/orelements described in connection with other embodiments unless otherwisespecifically indicated. Accordingly, it will be understood by those ofskill in the art that various changes in form and details may be madewithout departing from the spirit and scope of the present invention asset forth in the following claims.

What is claimed is:
 1. A flexible display apparatus, comprising: aflexible substrate including a display area and a bending area outsidethe display area, the bending area to be bent around a bending axis; aninorganic insulating layer on the flexible substrate; a cut unit in theinorganic insulating layer in the bending area; a stress relaxationlayer filling the cut unit and extending into the display area; a wiringpart on the stress relaxation layer in the bending area; a planarizationlayer covering the wiring part and on the stress relaxation layer; adisplay on the planarization layer in the display area and electricallyconnected to the wiring part; and a thin film transistor located in thedisplay area, the thin film transistor including a source electrode anda drain electrode, wherein the stress relaxation layer includes an uppersurface that is higher than or equal to an upper surface of the sourceelectrode and an upper surface of the drain electrode, and directlycontact a lower surface of the wiring part.
 2. The flexible displayapparatus as claimed in claim 1, wherein, the wiring part includes thesame material as the source electrode and the drain electrode of thethin-film transistor.
 3. The flexible display apparatus as claimed inclaim 1, wherein, the stress relaxation layer includes an opening, andthe source electrode and the drain electrode of the thin-film transistoris in the opening.
 4. The flexible display apparatus as claimed in claim1, wherein, in the display area, the planarization layer is on thestress relaxation layer.
 5. The flexible display apparatus as claimed inclaim 1, wherein the cut unit extends in a direction parallel to thebending axis.
 6. The flexible display apparatus as claimed in claim 1,wherein the stress relaxation layer includes an organic insulatingmaterial.
 7. The flexible display apparatus as claimed in claim 1,wherein a thickness of the stress relaxation layer in the cut unit isgreater than a depth of the cut unit.
 8. The flexible display apparatusas claimed in claim 1, wherein a lower surface of the stress relaxationlayer in the cut unit is in direct contact with an upper surface of theflexible substrate.
 9. The flexible display apparatus as claimed inclaim 1, wherein the planarization layer includes an organic insulatingmaterial.
 10. The flexible display apparatus as claimed in claim 1,wherein: in the display area, the thin-film transistor electricallyconnects the display to the wiring part, and a distance from an uppersurface of the planarization layer to the flexible substrate in a regionoverlapping the thin-film transistor is substantially the same as adistance from the upper surface of the planarization layer to theflexible substrate in a region overlapping the cut unit.
 11. Theflexible display apparatus as claimed in claim 1, wherein the flexiblesubstrate includes: a first substrate including a polymer resin; asecond substrate on the first substrate and including a polymer resin;and a barrier film between the first substrate and the second substrate.12. The flexible display apparatus as claimed in claim 11, wherein, inthe cut unit, a lower surface of the stress relaxation layer is indirect contact with an upper surface of the second substrate.
 13. Atouch-detecting display apparatus, comprising: a flexible substrateincluding a display area and a bending area outside the display area,the bending area to be bent around a bending axis; an inorganicinsulating layer on the flexible substrate; a stress relaxation layerfilling a cut unit in the inorganic insulating layer in the bendingarea, and extending into the display area; a wiring part on the stressrelaxation layer in the bending area; a planarization layer covering thewiring part and on the stress relaxation layer; a display on theplanarization layer in the display area and electrically connected tothe wiring part; a thin film transistor located in the display area, thethin film transistor including a source electrode and a drain electrode;a flexible encapsulation part covering the display; and a touchdetection layer on the flexible encapsulation part, wherein the stressrelaxation layer includes an upper surface that is higher than or equalto an upper surface of the source electrode and an upper surface of thedrain electrode, and directly contact a lower surface of the wiringpart.
 14. The touch-detecting display apparatus as claimed in claim 13,wherein, the wiring part includes the same material as the sourceelectrode and the drain electrode of the thin-film transistor.
 15. Thetouch-detecting display apparatus as claimed in claim 13, wherein, thestress relaxation layer includes an opening, and the source electrodeand the drain electrode of the thin-film transistor is in the opening.16. The touch-detecting display apparatus as claimed in claim 13,further comprising: color filters on the touch detection layer; and ablack matrix between the color filters.
 17. The touch-detecting displayapparatus as claimed in claim 13, wherein: the display includes a firstelectrode, an organic light-emitting layer, and a second electrode, anda tilt angle of the first electrode with a plane parallel to theflexible substrate is smaller than 0.1°.
 18. The touch-detecting displayapparatus as claimed in claim 13, wherein, in the display area, theplanarization layer is on the stress relaxation layer.
 19. Thetouch-detecting display apparatus as claimed in claim 13, wherein thecolor filters and the black matrix share an overlapping area.
 20. Thetouch-detecting display apparatus as claimed in claim 13, wherein: a padelectrode electrically connected to the wiring part is at an edge of theflexible substrate, and when the bending area is bent, the pad electrodeoverlaps the display area.
 21. The touch-detecting display apparatus asclaimed in claim 13, wherein a thickness of the stress relaxation layerin the cut unit is greater than a depth of the cut unit.
 22. Thetouch-detecting display apparatus as claimed in claim 13, wherein: inthe display area, the thin-film transistor electrically connects thedisplay to the wiring part, and a distance from an upper surface of theplanarization layer to the flexible substrate in a region overlappingthe thin-film transistor is substantially the same as a distance fromthe upper surface of the planarization layer to the flexible substratein a region overlapping the cut unit.